[PATCH][RFC] Allow to use adler32 for SCTP

Hi,

with OpenBSC I have to connect to some equipment that is configured to use
adler32 as the checksum. I wonder if something a long the lines of this patch
is acceptable? It adds a module parameter that globally allows to use adler32
and then there is a sockopt to enable adler32 on a per process basis. For the
receive path I have to decode both checksums.

I could probably just use the code to disable checksums for rx but I will need
to generate them on tx to make the other equipment accept these.

regards
	holger

PS: While adding my field to struct sctp_sock I saw that there are quite some
holes (on both ia32,x86_64) in the struct and that one can save 16byte by
re-ordering. I am not sure how to and if to benchmark such a change. Does it
make sense to re-order those?